The present application relates to a hydraulic wrench and especially to a hydraulic wrench for limited space applications, that is to applications in which the polygonal head of a threaded connector which has to be tightened or loosened by the wrench is located in a space which is rather limited about the axis of the threaded connector and above the polygonal head to be tightened or loosened thereon. In such limited space applications hydraulically operated wrenches as for instance disclosed in the U.S. Pat. No. 4,027,561 could not be used and it was up to now common practice to use a common flat wrench having at one end a passage of polygonal cross-section for engagement with a polygonal head of a threaded connector and a handle projecting from the aforementioned one end of the wrench and in which hammer blows have been exerted onto the free end of the handle to tighten or loosen the polygonal head of the threaded connector. The disadvantage of this known arrangement is of course, that the force at which a series of polygonal heads have been tightened on the threaded connectors depends on the force of the hammer blows and evidently a uniform tightening of a series of polygonal heads on a series of threaded connectors could not be assured.